Secondary batteries commercially available at the present include nickel-cadmium batteries, nickel hydrogen batteries, nickel-zinc batteries, lithium secondary batteries and the like. Among them, the lithium secondary batteries are in the limelight since they have almost no memory effect compared to nickel-based secondary batteries and also have very low self-discharging rate and high energy density.
The lithium secondary battery mainly uses lithium-based oxide and carbonaceous material as a positive electrode active material and a negative electrode active material, respectively. The lithium secondary battery includes an electrode assembly in which a positive electrode plate and a negative electrode plate respectively coated with a positive electrode active material and a negative electrode active material are disposed with a separator being interposed therebetween, and an exterior in which the electrode assembly is accommodated and sealed together with an electrolyte.
Generally, a lithium secondary battery may be classified into a can-type secondary battery in which an electrode assembly is included in a metal can and a pouch-type secondary battery in which an electrode assembly is included in a pouch made of aluminum laminate sheets, depending on the shape of an exterior.
In recent years, secondary batteries have been widely used not only in small-sized devices such as portable electronic devices but also in medium-sized and large-sized devices such as vehicles and power storage devices. When being used in medium-sized and large-sized devices, a large number of secondary batteries are electrically connected to increase capacity and power. In particular, pouch-type secondary batteries are widely used for the medium-sized and large-sized devices since they are easy to be stacked. In addition, as a plurality of secondary batteries are accommodated in a pack case, a battery pack may be constructed.
Various characteristics are required for the battery pack, and a representative characteristic is safety. Further, the safety of the battery pack mounted on a vehicle is very important because it is directly related to the life of a passenger.
In particular, one of the important issues with regard to the safety of the battery pack is the direct exposure to flame. In the case of a battery pack, it is a priority to prevent a fire inside, but in some cases, a fire may occur inside the battery pack. At this time, in a conventional battery pack, the flame and gas generated from the fire occurring therein are discharged to the outside, which may cause a large fire and break or damage internal parts of the battery pack and other components around the battery pack. In particular, if a fire occurs in the battery pack mounted on a vehicle, the fire may be very dangerous to passengers. Further, when the battery pack is mounted on a hybrid vehicle or collided with another vehicle, if a fuel storage tank is exposed to flame or hot gas, the fuel may explode, which may lead to a major accident.